Back to EveryPatent.com
| United States Patent |
6,063,730
|
|
Simpson
, et al.
|
May 16, 2000
|
Reusable donor layer containing dye wells for continuous tone thermal
printing
Abstract
A reusable thermal dye donor element for a dye transfer thermal printer
comprising: a base support having a plurality of wells which
preferentially adsorb and desorb dye; and an overcoat on the base support
which has a thickness less than the depth of the plurality of wells.
| Inventors:
|
Simpson; William H. (Pittsford, NY);
Dawson; Susan L. (Pittsford, NY);
Gray; Maurice L. (Rochester, NY);
Brock; George W. (La Jolla, CA)
|
| Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
| Appl. No.:
|
136724 |
| Filed:
|
August 19, 1998 |
| Current U.S. Class: |
503/227; 428/304.4 |
| Intern'l Class: |
B41M 005/035; B41M 005/38 |
| Field of Search: |
8/471
428/195,913,914,212,304.4,421,422,473.5
503/227
|
References Cited
U.S. Patent Documents
| 4661393 | Apr., 1987 | Uchiyama et al. | 428/200.
|
| 4695288 | Sep., 1987 | Ducharme | 8/471.
|
| 4737486 | Apr., 1988 | Henzel | 503/227.
|
| 5137382 | Aug., 1992 | Miyajima | 400/202.
|
| 5286521 | Feb., 1994 | Matsuda et al. | 427/146.
|
| 5334574 | Aug., 1994 | Matsuda et al. | 503/227.
|
| 5885929 | Mar., 1999 | Brock et al. | 503/227.
|
Primary Examiner: Hess; Bruce H.
Attorney, Agent or Firm: Noval; William F.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This patent application claims the benefit under 35 USC .sctn.120 of the
earlier filing date of U.S. patent application Ser. No. 08/877,387, filed
Jun. 17, 1997.
Claims
What is claimed is:
1. A reusable thermal dye donor element for a dye transfer thermal printer
comprising:
a base support with donor structure having a plurality of wells which
preferentially adsorb and desorb dye; and
an overcoat on said base support which has a thickness less than the depth
of said plurality of wells.
2. The donor element of claim 1 wherein said base support is a polyimide.
3. The donor element of claim 1 wherein said base support includes a base
layer and a donor layer having said plurality of wells.
4. The donor element of claim 1 wherein said overcoat is of
polytetrafluoroethylene.
5. The donor element of claim 1 wherein said plurality of wells have dye
incorporated into said wells without a binder.
6. The donor element of claim 5 wherein said dye is fused in said wells.
7. The donor element of claim 1 including a slip layer on said base
support.
8. A thermal dye transfer printing system comprising:
a reusable thermal dye donor element including a base support with donor
structure having a plurality of wells which preferentially adsorb and
desorb dye, and an overcoat on said base support which has a thickness
less than the depth of said plurality of wells;
a printing station at which dye is image-wise transferred from said dye
donor element to a receiver medium, at least partially depleting the dye
donor element of dye; and
a dye replenishment station for replenishing dye which has been depleted
from said donor element wells.
Description
FIELD OF THE INVENTION
This invention relates generally to thermal dye transfer printers and
relates more particularly to such printers having a reusable dye donor
member.
BACKGROUND OF THE INVENTION
As illustrated in FIG. 1, the major components of a thermal dye transfer
printing system are:
1. The print head 10, which contains an array of discrete resistors to
supply heat or electrodes to provide current with the heat generation via
Joule heating.
2. The donor sheet 12 which consists of a thin base film carrying a dye
material on one side and a slip layer on the side sliding against the
print head. For Joule heating in the belt, a current return layer is
required. The base has to be electrically conductive. Sheet 12 is fed
between donor supply 11 and donor take-up 13.
3. A receiver material 14 (such as paper or transparency) in intimate
contact with the dye side of the donor sheet.
4. A platen roller 16 required to form an intimate contact nip between the
print head, the dye donor and image receiver, to enable transfer of the
dye from the donor to the receiver, when the pulsed heat is generated
either in the ribbon 12 or the print head 10.
FIG. 2 shows resistive ribbon printing where electrodes 18 inject current
into the donor ribbon 20 where it heats the ink 22 and transfers it to the
receiver 24.
A significant problem in this technology is that the dye donor members used
to make the thermal prints are generally intended for single (one time)
use. Thus, although the member has at least three times the area of the
final print and contains enough dye to make a solid black image, only a
small fraction of this dye is ever used.
After printing an image, the dye donor member cannot be easily reused,
although this has been the subject of several patents. The primary reason
that inhibits reuse of the dye donor members is that the dye transfer
process is very sensitive to the concentration of dye in the donor layer.
During the first printing operation, dye is selectively removed from the
layer thus altering its concentration. In subsequent printings, regions of
the donor member which had been previously imaged have a lower transfer
efficiency than regions which were not imaged. This results in a ghost
image appearing in subsequent prints.
The cost associated with having a single use donor ribbon is large because
of the large area of ribbon required, as well as the large excess of dye
remaining coated on the donor member. While this technology is able to
produce high quality continuous tone color prints, it is desired to
provide an approach which has all of the good attributes of thermal dye
transfer imaging but without the limitations associated with single use
donor members.
Some work has been done by others to accomplish similar goals. For example,
U.S. Pat. No. 5,286,521 discusses a reusable wax transfer ink donor
ribbon. This process is intended to provide a dye donor ribbon that may be
used to print more than one page before the ribbon is completely consumed.
U.S. Pat. No. 4,661,393 describes a reusable ink ribbon, again for wax
transfer printing. The ink ribbon contains fine inorganic particles and
low melting waxy materials to assist in the repeated use of this ribbon.
U.S. Pat. No. 5,137,382 discloses a printer device capable of re-inking a
thermal transfer ribbon. However, again the technology is wax transfer
rather than dye transfer. In the device, solid wax is melted and
transferred using a roller onto the reusable transfer ribbon.
U.S. Pat. No. 5,334,574 describes a reusable dye donor ribbon for thermal
dye transfer printing. This reusable ribbon has multiple layers containing
dye and binder which limit the diffusion of dye out of the donor sheet.
This enables the ribbon to be used to make multiple prints. This enables
the ribbon to be used to make multiple prints. The binder provides the
medium through which the dye diffuses. Since the mass of dye is
transferred by diffusion a continues tone can be achieved by heating the
dye/binder to several levels of temperature thus providing a plurality of
density levels in the print.
The cross-referenced application discloses a printing engine which includes
a reusable thermal dye donor element having a base layer, and a donor
layer on the base layer which contains wells which preferentially adsorb
and desorb dye. The advantages of the invention described are a reusable
dye donor element which reduces cost and complexity in addition to the
minimization of environmental issues by a significant reduction in waste
product. The reusable belt described contains the wells entirely within
one layer such that the thickness of the pore layer is that necessary to
act as a well. The description of the reusable belt indicates that a
binder for the dye is not necessary. It would be anticipated by one
familiar with the state of the art that an oleophilic dye contained in the
well, when fused by heat, would behave in a manner similar to that of a
mass transfer system. That is, the transfer of the dye mass would be
binary since the dye is either in a fused state or unfused state. In this
case, it would require a half-tone printing method to produce prints which
have a plurality of density levels.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a solution to the
needs discussed above.
According to an aspect of the present invention, there is provided a
reusable thermal dye donor element for a dye transfer thermal printer
comprising: a base support having a plurality of wells which
preferentially adsorb and desorb dye; and an overcoat on the base support
which has a thickness less than the depth of the plurality of wells.
According to another aspect of the present invention, there is provided a
thermal dye transfer printing system comprising: a reusable thermal dye
donor element including a base support having a plurality of wells which
preferentially adsorb and desorb dye, and an overcoat on the base support
which has a thickness less than the depth of the plurality of wells; a
printing station at which dye is image-wise transferred from the dye donor
element to a receiver medium, at least partially depleting the dye donor
element of dye; and a dye replenishment station for replenishing dye which
has been depleted from the donor element wells.
ADVANTAGEOUS EFFECT OF THE INVENTION
The invention has the following advantages.
1. The dye donor element in a thermal printing system can be reused,
reducing cost and complexity of the system.
2. Environmental issues are minimized by a significant reduction in waste
product.
3. A continuous tone image of improved density and dynamic range is
obtained instead of a binary one.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view of a conventional resistive head thermal
printing system.
FIG. 2 is a perspective diagrammatic view of a resistive ribbon thermal
printing system.
FIG. 3 is a diagrammatic side view of a reusable dye donor element and
thermal printing system.
FIG. 4 is a diagrammatic side view of a segment of the dye donor element of
FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 3, there is shown a reusable dye donor element, such as
in the form of a belt 110 that is trained about a pair of rollers 112 and
114. At least one of the two rollers is driven to advance belt 110 past a
plurality of dye reservoir rollers 116, 118, and 120; one or more re-ink
heads 122; and a printhead 124 at a printing station.
Donor member belt 110 comprises a support 126 and a dye donor element such
as a plurality of dye donor patches 128, 130, and 132. Any material can be
used as the support for the dye-donor element of the invention provided it
is dimensionally stable and can withstand the heat generated. Such
materials include aluminum or other metals; polymers loaded with carbon
black; metal/polymer composites such as polymers metalized with 500-1000
.ANG. of metal; polyesters such as polyethylene terephthalate,
polyethylene naphthalate, etc.; polyamides (such as nomex);
polycarbonates; cellulose esters such as cellulose acetate; fluorine
polymers such as poly(vinylidene fluoride) or
poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as
polyoxymethylene; polyacetals; polyolefins such as polystyrene,
polyethylene, polypropylene or methylpentene polymers; and polyimides such
as polyimide-amides and polyether-imides. The support generally has a
thickness of from about 5 .mu.m to about 200 .mu.m and may also be coated
with a subbing layer, if desired, such as those materials described in
U.S. Pat. Nos. 4,695,288 or 4,737,486.
In the illustrated embodiment, the dye donor element forms a distinct dye
donor patch on the support for each color. However, a continuous dye donor
element over the entire support surface may be used, with machine logic
subdividing the single element into dedicated color regions. Likewise,
more than three patches may be used. (The dye donor element is described
below with respect to FIG. 4.)
Referring again to FIG. 3, conventional dye receiver medium 134 is drawn
through a nip formed between printhead 124 and a platen roller 136 by a
capstan drive roller pair 138 and 140. Dye receiver medium 134 is
conventional, and includes a support 142 and a receiving layer 144.
Image-wise activation of linear printhead 124 causes dye to be transferred
from the dye donor element of belt 110 into the dye receiving layer 144 of
medium 134; at least partially image-wise depleting portions of the
patches of dye.
Dye reservoir rollers 116, 118, and 120 include a permeation membrane.
Examples of membrane material include cellulose and derivatezed cellulose
used alone or blended with other components, polyesters, polyamides,
polysufone, crosslinked polystyrene, phenol/formaldehyde resin and
fluorinated polymers to include polytetrafluoroethuylene and
polyvinylidene fluoride, polycarbonate, poly(vinyl alcohol) and silicon
containing polymers. Membranes can be constructed from a dense layer of
polymer supported on a porous sub-layer. These polymeric membranes can be
crosslinked to further reduce permeability.
Dye reservoir rollers 116, 118, and 120 may be replaced by wicks formed of
similar materials, but not mounted for rotation.
Each dye reservoir roller is opposed by a re-ink head 122 (only one head is
illustrated in the drawing), and the rollers are selectively raised and
lowered into contact with belt 110 as necessary. When a dye reservoir
roller is lowered to the belt, and the associated re-ink head activated,
heat and/or pressure between the dye reservoir roller and belt 110 effects
re-inking of the dye donor element, and the depleted dye donor layer of
the patch is re-saturated with dye from the dye reservoir roller.
In this method, dye is thermally transferred from a reservoir to the
depleted donor patch. The dye and a carrier are contained in the
reservoir. The reservoir is covered with a diffusion controlled permeation
membrane. With the addition of heat dye diffuses through the membrane and
is delivered to the donor patch. The dye partitions between the reservoir
and the donor patch reestablishing the original dye concentration.
FIG. 4 shows the structure of the dye donor element according to the
invention. As shown, dye donor element 200 includes
1. A slip layer 202,
2. A base film (such as polyimide) 204,
3. An under-layer 206,
4. A pore layer 208 having wells 210, and
5. An overcoat layer 214.
In one embodiment, using an oil based dye formulation, the under-layer 206
is a very thin layer of oleophilic material. The thickness of the pore
layer 208 is that necessary to act as a well for the resulting design, and
pore layer material is oleophobic.
In another embodiment, the alternate situation is where the dye formulation
is water based and the top surface of the under-layer 206 is wetted by
water (oleophobic) and the surface of the pore layer 208 is not wetted by
water (oleophobic).
The under-layer 206 may be metal, metal oxide, or polymer. It can provide
the current return path for a resistive ribbon printing system. The
pore-layer 208 is a polymer that has wells 210 formed through it to expose
the surface of layer 206. It is preferably a hard wearing surface, that
can be coated and is initially non cross-linked, and can have holes formed
through it, and then heated to cross link it. Alternatively, the pore
material 208 may be a UV curable system and after the well formation, is
cross-linked by UV radiation.
Methods of forming the wells 210 in pore material 208 include:
a) laser ablation down to the surface of layer 206, which should be chosen
to be non-absorbing by the laser beam wave length.
b) the pore layer surface 212 can be coated with photoresist and exposed to
arrays of wells through masking, through which chemical attack forms holes
in the pore layer 208, and the photoresist in subsequently removed. It is
possible that layer 208 itself could be photoresist, which after well
formation through it, can be heat or UV cross linked to form a wear
resistant surface.
The dimensions of the well can be controlled by the pore-layer 208
thickness, and well diameter. The degree of surface tension from well
capillary action and surface wetting at the well bottom is controlled by
the diameter of the well, these must be balanced against the dye
properties to attract sufficient dye into the wells in layer 208. The well
pitch can be determined from dye requirements for printing.
Overcoat layer 214 can be a polyimide layer having a thickness less than
layer 208.
Following is a more detailed description of the present invention.
A. Laser Indented Donor Support:
Control Example 1 consists of a polyimide sheet (Kapton.RTM. sheet (E.I.
DuPont de Nemours)) approximately 0.002 inches thick which has been
indented by the procedure discussed below. The wells or blind holes are
placed in a close-packed hexagonal array. The holes are 2 microns deep and
approximately 7 microns in diameter. The wells are filled with Dye mixture
"A".
Control Example 2 is the same as Control Example 1 except that the holes
are 1 micron deep and 5 microns in diameter.
Control Example 3 is the same as Control Example 2 except that it was
filled with Dye mixture "B".
Invention Example 1 consists of the same polyimide sheet as Control Example
1 except that the sheet has been overcoated with a polytetrafluoroethylene
polymer (PTFE) (Teflon.RTM. polymer(120FN 616 from DuPont)). The size of
the wells and dye mixture used are the same as that in Control Example 1.
Invention Example 2 consists of the same polyimide sheet as Control Example
2 except that the sheet has been overcoated with a PTPE polymer. The size
of the wells and dye mixture used are the same as that in Control Example
2.
Invention Example 3 is the same sample as that used in Invention Example 2
except that the dye-filled, indented donor was treated with a fusing step
(vide infra-printing) prior to actually printing the dye to a thermal dye
receiver.
Invention Example 4 consists of the same polyimide sheet as Control Example
3 except that the sheet is overcoated with a PTFE polymer. The size of the
wells and dye mixture used are the same as that in Control Example 3.
B. Procedure for preparing wells in donor support
The well-patterned polyimide donor used in the printing experiments was
produced using photolithography and ion etching. The PTFE coated polyimide
sample was laminated to a silicon wafer and coated to a thickness of 2
microns with Hoechst-Celanese AZ 1518 photoresist. The hole pattern was
exposed on the photoresist through a mask, using a standard photoresist
aligner, and holes developed through the photoresist coating. The
resulting photoresist surface was ion-milled for a sufficient time to
produce one micron deep, blind holes (wells) through the PTFE into the
polyimide surface. The remaining photoresist was stripped off the milled
polyimide surface and the samples removed from the silicon wafer. Each
sample was prepared in a similar manner regardless of composition. The
holes or wells can be placed in the sample using many different designs,
such as a linear array or close-packed hexagonal.
C. Procedure for filling wells with dye
Dye Mixture "A" was prepared by blending 21 weight percent Dye 1, 29% Dye 2
and 50% Dye 3 into a homogenous mixture.
Dye Mixture "B" was prepared by blending 23 weight percent Dye 3, 39% Dye
4, 38% Dye 5 into a homogenous mixture
A laboratory hot-plate (PL-351 from Corning, Inc.) was used to heat the
sample of indented donor to between 125 and 135 degrees Celsius. A copper
plate (8".times.10".times.1") was placed on top of the hot plate. A glass
plate (6.times.6.times.1/2") was then placed over the copper plate. The
indented donor was cut to 1.times.3 inches and taped to a glass microscope
slide with the empty wells facing outward. The glass slide with mounted
donor was heated on the hot plate assembly above. A small amount of either
Dye Mixture "A" or "B" was placed on the face of the indented donor and
allowed to fuse. The fused dye was spread evenly over the surface with a
wooden spatula. The excess dye mixture was removed from the surface by
wiping with a clean, cotton cloth while the donor remained on the hot
plate assembly. The sample was removed from the hot plate assembly and
allowed to cool. After cooling the cleanliness of the surface and filling
of the wells was evaluated by optical microscopy. The surface was found to
be clean of excess dye and the wells filled. The resulting samples were
then printed to a thermal dye receiver using the procedure below.
While the procedure above represents a manual method for filling the
indented donor with dye it should be obvious to one skilled in the state
of the art that automated mechanical and electrical methods can be devised
to accomplish the same purpose.
D. Procedure for printing dye filled donor support to receiver
All images made with the dye-filled, laser indented donors were printed
under identical conditions. Each of the thermally transferred reflection
images was composed of a step wedge gradient printed down the length of
the receiver. An X-Rite densitometer (X-Rite Inc., Grandville, Mich.)
measuring Status A reflection density was used to determine differences in
printing efficiency.
The imaged prints were prepared by placing the indented dye-donor element
which had been filled with dye previously, in contact with the polymeric
receiving layer side of the receiver element. A Mylar.RTM. (E.I. DuPont de
Nemours) substrate six micrometers thick with a slipping layer was placed
over the indented donor such that the slipping layer is in contact with
the thermal print head. The entire assemblage was fastened to the top of
the motor driven 53 mm diameter rubber roller and a TDK thermal head
L-231, thermostated at 30.degree. C. with a head load of 2.5 Kg pressed
against the rubber roller. (The TDK L-231 thermal print head has 512
independently addressable heaters with a resolution of 5.4 dots/mm and an
active printing width of 95 mm, of average heater resistance 501 ohms).
The imaging electronics were activated and the assemblage was drawn
between the printing head and roller at 20.6 mm/sec. Coincidentally, the
resistive elements in the thermal print head were pulsed on for 114
microseconds every 130 microseconds. Printing maximum density requires 128
pulses "on" time per printed line of 17 msec. The images were printed with
a 1:1 aspect ratio. The maximum printing energy was 10.2 J/cm.sup.2.
A fusing step was employed in one experiment where the applied voltage on
the print head was raised to 13 volts. At the same time the resistive
elements were pulsed on for 128 microseconds every 130 microseconds. The
fusing energy was 19.3 J/cm.sup.2.
E. Receiver formulation
The dye receiving element consisted of a subbed reflective base material,
as described in U.S. Pat. No. 5,244,861, coated with a dye-receiving layer
comprising Makrolon.RTM.KL3-1013 (Bayer AG) (1.71 g/m.sup.2) and Lexan
141.RTM. (General Electric Co.) (1.40 g/m.sup.2), Drapex 429.RTM. (Witco)
(0.26 g/m.sup.2), diphenylphthalate (Eastman Kodak Co.) (0.52 g/m.sup.2),
Fluorad FC-431.RTM. (3M Corp.) (0.012 g/m.sup.2) was coated from
dichloromethane. This receiver layer was overcoated with a polymeric layer
consisting of KGH(50)HA(6.5wt %)PDMS (Eastman Kodak Co.) (0.66 g/m.sup.2),
KGH(50)HA polyol (Eastman Kodak Co.) (0.108 g/m.sup.2), Fluorad
FC-431.RTM. (0.022 g/m.sup.2) and DC-510 (Dow Corning Co.) (0.0027
g/m.sup.2) dissolved in dichloromethane.
TABLE I
______________________________________
Status A Density of Step Wedge Image with Dye Mixture "A"
Invention Invention
Invention
Control Example 1
Control Example 2
Example 3
Steps
Example 1 Overcoat Example 2
Overcoat
Overcoat
______________________________________
1 1.38 2.23 1.35 2.05 1.57
2 1.29 2.10 1.26 1.89 1.21
3 1.15 1.70 1.12 1.47 1.01
4 0.21 1.40 1.00 0.86 0.77
5 0.17 0.97 0.40 0.59 0.60
6 -- 0.64 0.17 0.28 0.37
7 -- 0.19 -- 0.17 0.19
8 -- 0.13 -- -- 0.05
______________________________________
TABLE II
______________________________________
Status A Density of Step Wedge Image with Dye Mixture "B"
Invention Example 4
Control Example 3 Overcoat
Steps Red Green Blue Red Green Blue
______________________________________
1 0.92 1.08 1.17 1.95 2.34 2.46
2 0.60 0.72 0.79 1.28 1.76 2.06
3 0.20 0.29 0.33 1.12 1.53 1.82
4 0.11 0.15 0.15 0.59 0.79 0.92
5 0.09 0.12 0.12 0.37 0.49 0.58
6 0.24 0.32 0.38
7 0.16 0.19 0.21
8 0.14 0.16 0.17
______________________________________
It can be seen from Table I that Invention 1 Examples 1 and 2 have higher
maximum densities and a larger number of steps compared to Control
Examples 1 and 2, respectively, when printed under the same conditions.
The results indicate that placing a PTFE coating on the polyimide
substrate improves the printed Status A density when the wells are filled
with Dye Mixture "A". Invention Example 3 has two additional steps when
compared to Control Example 2 which indicates that fusing the filled,
indented donor gives a longer dynamic range.
It can be seen from Table II that Invention Example 4 has a significantly
higher density and a larger number of steps than Control Example 3. The
results indicate that placing a PTFE coating on the polyimide substrate
improves the printed density and number of steps when the wells are filled
with Dye Mixture "B".
##STR1##
The invention has been described in detail with particular reference to
certain preferred embodiments thereof, but it will be understood that
variations and modifications can be effected within the spirit and scope
of the invention.
______________________________________
PARTS LIST
______________________________________
10 print head
11 donor supply
12 donor sheet
13 donor take-up
14 receiver material
16 platen roller
18 electrodes
20 donor ribbon
22 ink
24 receiver
110 donor member belt
112,114 rollers
116,118,120 dye reservoir rollers
122 re-ink heads
124 print head
126 support
128,130,132 dye donor patches
134 dye receiver medium
136 platen roller
138,140 capstan drive roller pair
142 support
144 receiving layer
200 dye donor element
202 slip layer
204 base film
206 under-layer
208 pore layer
210 wells
212 pore layer surface
______________________________________
Top